Application of kinetically labile complex equilibria to the separation of anions by isotachophoresis

The kinetics of complex equilibria are briefly discussed from the viewpoint of their use in isotachophoresis. The possibility of separating some anions on the basis of the kinetically labile complex equilibria was studied and the composition of leading electrolytes suitable for this type of separation is discussed. A successful separation of some anions that differ in their stability constants with Ca2+ illustrates the separation of anions according to stability constants

Project ILSAP: an inter-laboratory study on accuracy and precision in isotachophoresis

In a collaborative study by seventeen laboratories, six aqueous sample solutions also containing 0.9% (w/v) NaCl were analysed for lactate and creatinine using isotachophoresis. A split-level study was carried out with three levels of the order of 3, 10 and 30 mmol/l, two sublevels and without blind duplicates. A calibration graph was constructed at five concentrations, using citrate and Tris as internal standards, added on a mass basis. The concentrations in the sample were determined in singular. After elimination of a few outliers using the Grubbs test at a 1% confidence level, data were treated according to ISO 5725. For low, medium and high concentration levels, the repeatability values r were 0.41, 0.40 and 1.67 mmol/l, respectively, for lactate and 0.63, 0.53 and 1.43 mmol/l, respectively, for creatinine. The reproducibility values R were 0.59, 1.12 and 2.05 mmol/l, respectively, for lactate and 1.33, 0.88 and 2.66 mmol/l, respectively, for creatinine

Capillary zone electrophoresis with on-line isotachophoretic sample pretreatment : sample clean-up aspects

A theoretical model intended for characterizations of capillary zone electrophoresis (CZE) separations of samples of unknown matrix compositions with on-line isotachophoresis (ITP) sample pretreatment was developed. Assuming the use of the column-coupling capillary electrophoresis (CE) separation system, this model explicitly defines (i) potential sample interferents for a given CZE analyte in both stages of the ITP-CZE combination and (ii) residual sample interferents in the CZE stage, i.e., interfering sample constituents which cannot be removed from the sample by the ITP pretreatment using a particular combination of the ITP and CZE electrolyte systems. Relationships applicable to estimations of sizes of these groups of sample interferents are provided by the model. A calculation procedure based on these relationships was developed to test the model. The results from these tests obtained for a group of CZE analytes of different acid-base properties (p-sulfanilic acid, hippuric acid, 2,6-dinitrophenol, and o-nitrophenol) show that an effective use of the ITP-CZE combination in the column-coupling separation system requires (i) that the ITP and CZE electrolyte systems introduce different separation mechanisms for the analyte and (ii) that the size of the sample fraction in which the analyte is transferred into the CZE column after the ITP pretreatment is kept at a minimum. Numerical data obtained in these tests for p-sulfanilic acid were in reasonable agreement with the ones provided by computer simulations of the CZE and ITP-CZE separations with the sample matrix consisting of 264 anionically migrating constituents of known migration properties

Capillary zone electrophoresis with on-line isotachophoretic sample pretreatment : sample clean-up aspects

A theoretical model intended for characterizations of capillary zone electrophoresis (CZE) separations of samples of unknown matrix compositions with on-line isotachophoresis (ITP) sample pretreatment was developed. Assuming the use of the column-coupling capillary electrophoresis (CE) separation system, this model explicitly defines (i) potential sample interferents for a given CZE analyte in both stages of the ITP-CZE combination and (ii) residual sample interferents in the CZE stage, i.e., interfering sample constituents which cannot be removed from the sample by the ITP pretreatment using a particular combination of the ITP and CZE electrolyte systems. Relationships applicable to estimations of sizes of these groups of sample interferents are provided by the model. A calculation procedure based on these relationships was developed to test the model. The results from these tests obtained for a group of CZE analytes of different acid-base properties (p-sulfanilic acid, hippuric acid, 2,6-dinitrophenol, and o-nitrophenol) show that an effective use of the ITP-CZE combination in the column-coupling separation system requires (i) that the ITP and CZE electrolyte systems introduce different separation mechanisms for the analyte and (ii) that the size of the sample fraction in which the analyte is transferred into the CZE column after the ITP pretreatment is kept at a minimum. Numerical data obtained in these tests for p-sulfanilic acid were in reasonable agreement with the ones provided by computer simulations of the CZE and ITP-CZE separations with the sample matrix consisting of 264 anionically migrating constituents of known migration properties